Contributed paper
OPTO-ELECTRONICS REVIEW 11(1), 55–63 (2003)
Optimisation of construction of two-channel acousto-optic modulator
for radio-signal phase detection
L. JOD£OWSKI*
Institute of Optoelectronics, Military University of Technology
2 Kaliskiego Str., 00-908 Warsaw, Poland
Two-channel acousto-optic modulator (AOM) makes simultaneous assignment of the frequency and phase of radio-signals
possible. AOM is a fundamental element of a spectrum analyser based on acousto-optic receiver. In the paper, an analysis of
influence of structural elements on characteristics of a two-channel modulator was shown and the procedure of optimisation
of its construction described. Basing on this procedure the modulator for spectrum analysis at GSM band was designed, performed and investigated. The two-channel acousto-optic modulators give the possibility of detection and defining direction
of radiation with accuracy of 0.5°.
Keywords: acousto-optics, modulator, phase detection.
1. Introduction
Acousto-optic modulators (AOM) are based on elasto-optic
effect which allows transfer of information from acoustic
wave to light beam. AOM are commonly applied in RF signal analysers. The possibility of performing Fourier analysis of high frequency radio signal in real time is their major
advantage. Practical implementation of AOM is possible
since high sensitivity CCD linear arrays have been built.
Elaboration of CCD cameras enabled one to carry out
two-dimensional analysis of an image in a focus of analysing system. Thus, simultaneous analysis of frequency and
phase of radio signal became possible.
Two-channel acousto-optic modulator is an upgraded
version of acousto-optic deflector and was not described in
available literature [1,2]. Acousto-optic deflectors are used
in signal analysers [3,4] and broadband and fast signal
analyses [5] are their major advantages. Spectral analysis is
carried out in real time without any time delay. Acousto-optic modulator designed for measuring radio signal phase
contains, compared to deflector, a second channel (reference one) and signal is analysed in XY image plane. Like
for deflector, optimisation of construction consists in elaboration of main structural elements:
• active material and its orientation,
• optical aperture of modulator,
• material and orientation of piezoelectric transducer,
• central frequency and bandwidth of transducer,
• configuration and size of electrodes,
• matching circuits.
*e-mail:
[email protected]
Opto-Electron. Rev., 11, no. 1, 2003
The problem of cross-talk signals is difficult to predict
and is presented elsewhere [6]. Analysis of properties of
the two-channel modulator for structural optimisation is the
main goal of the paper.
2. Analysis of influence of structural elements on
characteristics of two-channel modulator
(deflector)
2.1. Characteristics of the modulator
An arrangement scheme for analysis of radio-signal phase
is shown in Fig. 1. Separated blocks represent: light source
(laser), beam forming optics, two-channel acousto-optic
modulator, analysing optics and elements of image registration and analysis (CCD camera, PC computer with
frame-grabber card). Collimating optics is used to obtain
uniform intensity distribution of laser beam in the area of
acousto-optic modulator’s part overtaken by acoustic
beam. As a result of acousto-optic effect part of laser
beam is deflected with an angle proportional to frequency
of electric signal. Analysing optics (lens) separates and
focuses deflected and main beams in different places, so
in an image plane of CCD camera only deflected beam is
visible.
A structural scheme of the two-channel acousto-optic
modulator is presented in Fig. 2(a). Interaction between
light beam and ultrasonic wave takes place in an acoustic
buffer region (1). Ultrasonic beam is generated and
formed by the piezoelectric transducer (2) with the electrodes (5) of dimensions d´l. The length of ultra-
L. Jod³owski
55
Optimisation of construction of two-channel acousto-optic modulator for radio-signal phase detection
Fig. 1. Scheme of a system for analysis of radio-signal phase with use of two-channel A-O modulator. In1 and In2 are the signal and
reference inputs, respectively.
Fig. 2. Details of construction of A-O modulator (a) and a CCD picture (b) taken in a laboratory setup.
sound-light interaction equals A (the width of optical window (4)). A distance between parallel electrodes is H. The
absorber (3) is intended for attenuation of acoustic wave
after having passed the whole buffer. An interference picture recorded by CCD camera is shown in Fig. 2(b). Projection of interference picture on x axis gives information
about frequency of signal utilised in a spectrum analyser.
Distribution of light intensity at y direction depends on
differences between phases of analysed and reference signals.
2.2. Buffer material, conversion efficiency, and
attenuation of acoustic wave
Q=
nV
,
(1)
where is l0 is the wavelength of light beam, l is the length
of ultrasound interaction (length of transducer), n is the index of refraction, F0 and V are the frequency and the velocity of ultrasound wave, respectively.
So, for Q < 1 Ramman-Nath mode of diffraction occurs
and for Q > 1 Bragg diffraction takes place. Bragg diffrac-
56
sin Q B =
l0
,
2L
(2)
where L is the wavelength of acoustic wave, and QB is the
Bragg angle.
Deflected beams appear in +1 or –1 diffraction orders
and they change their frequencies according to the following dependence
w1 = W + w 0
Bragg diffraction is used to describe phenomena in
acousto-optic deflectors [5]. A diffraction mode depends
on light and sound wave frequencies as well as on length of
interaction. The Cook parameter is a criterion for estimating a diffraction mode [1]
l 0 lF02
2
tion occurs when angles of incidence of both light and
acoustic beams fulfil Bragg condition
(for +1 order).
In linear regime (up to 60–70% of modulation) diffraction efficiency depends on energy of acoustic wave and
acousto-optical quality factor
2
a0
54 h d æ l ö
=
ç
÷ ,
Pe M 2 l è l1 ø
(3)
where l and d are the length and the width of transducer, respectively, M2 is the relative quality factor of buffer (compared with quality factor for fused quartz), l and l1 are the
wavelengths of applied and He-Ne lasers, respectively, h is
the diffraction efficiency and a0 is the efficiency of electric
energy conversion into acoustic wave energy.
In Table 1, data of materials chosen for acousto-optic
media are presented. The most important parameters are
Opto-Electron. Rev., 11, no. 1, 2003
© 2003 COSiW SEP, Warsaw
Contributed paper
Table 1. Characteristics of acusto-optic materials suitable for longitudinal wave propagation.
r´103
(kg/m3)
V´103
(m/s)
M2´1015
(c3/kg)
a
(dB/GHzcm)
l0
(µm)
T
Transparency
(µm)
n
Fused quartz
2.20
5.96
1.56
12
0.63
0.2–4.5
1.457
GaP
4.13
6.32
44.6
6
0.63
0.6–10
3.31
PbMoO4
6.95
3.63
36.3
15
0.63
0.42–5.5
0.42–5
TeO2
5.87
3.40
34.5
10
0.63
0.35–5
2.26
Ge
5.38
5.50
260
30
10.6
2.0–20
4
Te
5.25
2.29
5860
420
10.6
4.0–20
2.29
LiNbO3
4.63
6.57
7
0.15
0.63
0.4–4.5
2.29
SF41(CF 755-28)
4.79
3.76
7.2
110
0.63
0.4–4
1.75
SF81(CF 689-31)
4.21
3.89
6.3
50
0.63
0.4–4
1.685
SF141(CF 762-27)
4.51
14.059
5.6
35
0.63
0.4–4
1.756
BK 7
2.53
5.53
0.63
0.34–4
1.517
Material
1
measurements of attenuation [13] were made for 50–250 MHz band
the following: the quality factor M2, the attenuation of
acoustic wave a, and the range of optical transparency T.
For isotropic materials diffraction efficiency depends on
incidence angle of light beam and is the largest for Bragg
angle, so this condition occurs for one frequency only. For
higher and lower frequencies decrease in diffraction efficiency is observed and this can be compensated using external matching circuit (matching filter) [7].
Attenuation of acoustic wave in material decreases its
intensity with a increasing distance from transducer surface
and causes decrease in diffraction efficiency via limitation
of effective aperture. This phenomenon is strictly connected with deflector resolving power. As it was shown in
Ref. 1, a 25 dB attenuation at aperture region causes 30%
worsening of resolving power.
For acoustic powers less than optimal ones diffraction
efficiency meets twofold decrease if attenuation equals
8 dB at aperture region. Increasing acoustic power can improve it. So, after having attenuation compensated, a serious 40–50% improvement in diffraction efficiency can be
obtained for 10–20 dB attenuation at aperture region. As a
result, intensity of light decreases not more than 40–50%.
Piezoelectric crystals are commonly used for transducers converting electrical energy to mechanical one. Numerous investigations showed [8,9] that transducers based on
LiNbO3 crystals or on deposited TeO2 layers are the best
for longitudinal wave generation.
æ pl ö
DQ d = ç
÷ DF,
è nV ø
where l is the length of optic wave, p is the number of diffracted order, DF is the frequency band of acoustic wave, n
is the refractive index, and V is the acoustic wave speed.
The number N of resolved positions of deflected beam
depends on angular width jd of a light beam
N =
Opto-Electron. Rev., 11, no. 1, 2003
DQ d
.
jd
(5)
If jd angle depends only on diffracted effect connected
with a finite size of light beam, then
jd =
ml
nA
(6)
where µ is the parameter depending on a light beam structure and a criterion of resolving power, A is the size of the
light beam (aperture).
For instance, according to Rayleigh’s criterion the two
beams are considered as resolved if maximum of the first
beam overlaps with a minimum of the second one. Then
the parameter µ equals 1 for homogeneous rectangular
beam, while µ equals 1.22 for homogeneous circular beam
and µ equals 1.34 for Gaussian beam.
This criterion is very strict, so other criteria of resolution are also used. For rectangular light beam of homogeneous intensity distribution (µ = 1) we have
2.3. Resolving power of deflector
N =
Scanning angle of the deflector Dqd depends on acoustic
frequency band and is described as follows
(4)
DFA
= DFt
V
(7)
where t is the time-of-flight of acoustic wave passing aperture of deflector (t additionally defines switching rate).
L. Jod³owski
57
Optimisation of construction of two-channel acousto-optic modulator for radio-signal phase detection
Equation (7) relates two fundamental characteristics of
deflector: resolution and switching rate. Analysis of solution of the equation shows two ways for resolution improvement: increase in acoustic band or increase in light
beam size. However, the second way simultaneously decreases switching rate.
2.4. Interference of the deflected beams in a focus
If the lens aperture and focus are D and f, respectively, (see
Fig. 3(a), the light intensity distribution in a focus can be
described as follows
I ( y) = [sin c (x )] 2 ,
(8)
where function sinc(x) is the standard function:
sinc(x) = sinx/x.
The first minimum of intensity distribution occurs for
the angle b as
122
. l
.
(9)
b =
A
For small angles, b can be expressed as b = x f ; so the
function sinc has its first zero value for the argument
Py = p. If so, then
pd
,
(10)
P=
mlf
where d is the height of transducer, µ is the parameter of
distribution (described in previous section), l is the wavelength of light beam, and f is the lens focus. Both light
beams carrying information about acoustic signal phase interfere in a focus.
The distance between interference maxima depends on
heights H of beams and focal length of the analysing lens
[see Fig. 3(b)]. So, the function sinc is “modulated” by the
harmonic function (eg., cos) with an argument
æ
ö
H
y + j÷ ,
ç 2p
lf
è
ø
(11)
where H is the distance between the transducers and j is
the phase of acoustic signal.
Final formula for distribution of light intensity in a focus of analysing lens is the following
2
æ æ pd ö ö
y÷ ÷
ç sinç
è mlf ø ÷ é
öù
æ
H
ç
I ( y) =
1 + cosç 2p
y + j ÷ ú , (12)
ê
÷
ç
pd
lf
øû
è
y ÷ ë
ç
ø
è mlf
where d is the height of transducer, µ is the parameter of
distribution (described in previous section), l is the wavelength of light beam, f is the lens focus, H is the distance
between transducers, and j is the phase of the acoustic signal.
2.5. Central frequency and transducer bandwidth
From generator side, piezoelectric transducer has complex
impedance [10]. Electric matching between transmitter
(generator) and receiver (transducer) is necessary to ensure
optimal propagation of electric energy. Since input impedance of the transducer is a complex function of structural
parameters (including also acoustic and mechanical properties of layers connecting piezoelectric transducer and a
buffer) the analysis of the system is not simple [11,12]. In
general, surface of the transducer and a difference in acoustic impedances between the transducer and the buffer have
major influence on band narrowing. Even using matching
G type circuits, different electric bandwidths can be obtained for the same transducer. Details are presented in
Ref. 12.
An equivalent circuit described by Mason [10] was applied to carry out an analysis of transducer’s electric impedance. Figure 4(a) shows a scheme of transducer for
analysis of electric impedance. Transducer plate of thickness d and of acoustic impedance Z0 is placed between the
waveguide and absorber of impedances Zb and Za, respectively. The voltage e3 is connected to terminals 3–3 and the
current i3 is flowing through the transducer. Equivalent
scheme of the transducer is shown in Fig. 4(b). According
to equivalent scheme quantities characterising the transducer and adjacent media are transformed into the electric
impedance.
For one-sided load (buffer loaded by Zl impedance), input impedance can be described as follows
æ
1 ö
Z = R3 + j ç X 3 ÷ ,
wC 0 ø
è
(13)
where
2
æf ö
R3 = Ra ç 0 ÷ H r ,
è fr ø
(14)
2
Fig. 3. Light intensity distribution in a focus (a) and interference
pattern (b) from sources positioned at a distance H.
58
Opto-Electron. Rev., 11, no. 1, 2003
æf ö
X 3 = Ra ç 0 ÷ H i ,
è fr ø
(15)
© 2003 COSiW SEP, Warsaw
Contributed paper
Fig. 4. Piezoelectric transducer. Transducer scheme (a) and equivalent scheme (b).
Ra =
Hr =
1 æ Zl ö
ç
÷
4 è Z0 ø
2
p Z0 k0
,
4 Z l v 0C 0
2
[1 - cos(kd )] 2
æZ
ö
[sin(kd )] 2 + ç l cos(kd )÷
è Z0
ø
2
,
ö
æ æ1 æ Z ö 2
ö
ç
sin(kd ) 1 + ç ç l ÷ - 1÷ cos(kd )÷
ç
÷
ç
÷
ø
ø
è è2 è Z0 ø
1 Zl
,
Hi =
2
2 Z0
æ Zl
ö
2
[sin(kd )] + ç
cos(kd )÷
è Z0
ø
and
kd = p
f
,
f0
f0 =
V
,
2d
C 0 = e 0e w
(17)
(18)
Rg
Z
,
(19)
where Rg is the resistance of generator (usually 50 W) and
Z is the load impedance.
Standing wave ratio (SWR) is defined as follows
SWR =
1+ G
,
1- G
(20)
where G = (1 - r ) (1 + r ).
Expressing load impedance in a normalised form as Z =
R + jX, the quantity G can be expressed by real and imaginary parts of the impedance
S
.
d
G =
In Eqs. 13–18, influence of the connecting layers on
electric impedance of the transducer was neglected. The influence of connecting layers can be neglected up to the frequencies 100–150 MHz for metallic layers of 1-µm thickness. For higher frequencies an influence of the layers must
be taken into consideration [11].
2.6. Electrical matching between transducer and
measuring circuit
Parallel or series inductive coil can be used as a matching
circuit for some cases. Although transducer operation without matching circuit is possible such solution is used for
acoustic measuring heads rather than for acousto-optic
modulators [12]. Since full impedance matching for the
transducer occurs for chosen frequencies only, a suitable
criterion for evaluation of matching is based on, so called,
standing wave ratio (SWR). This parameter is measured in
a typical operational mode of network analysers. Reflection
coefficient r of incident wave depends on load impedance
Opto-Electron. Rev., 11, no. 1, 2003
r =
(16)
( R2 - 1 + X 2 ) 2 + 4 X 2
( R + 1) 2 + X 2
(21)
A criterion for sufficient matching for the transducer is
SWR < 1.5. When receiver impedance and circuit impedance are fully matched SWR equals 1, while for short and
open circuits it reaches infinity. For example, for 3dB electric band attenuation SWR amounts 6.
On the other hand, insufficient impedance matching
leads to reflection of electric power at impedance drop and
as a result significantly lower electric power is delivered to
the circuit. Moreover, time of oscillations fading increases
and a deformation of pulse shape is observed. It is particularly undesirable for short pulses when the period of oscillations fading and pulse duration at impedance discontinuity are comparable
ti £
g
,
V
(22)
where g is the thickness of transducer and V is the speed of
sound in transducer.
L. Jod³owski
59
Optimisation of construction of two-channel acousto-optic modulator for radio-signal phase detection
A frequency shift for maximum radiation towards lower
frequencies is another effect observed for loaded transducer, so the optimal thickness of transducer g is smaller
than that calculated for free oscillations (l/2)
g £
V
.
2 F0
(23)
Example: for 20 MHz frequency pulse deformation is observed for 25 ns pulses, while for higher frequencies deformation occurs for shorter pulses.
In many cases the single-element G filters can be used
as matching circuits. A bandwidth of matched transducer
depends on its impedance and filter configuration. More
detailed analysis showed that larger bandwidth of electrical
matching can be obtained when real part of transducer impedance is close to impedance of generator (transmitting
line) [12]. In calculations, both parallel and series equivalent circuits must be taken into account. Generally, four basic configurations of G type matching circuits must be analysed to make a proper choice of optimal configuration
[11].
The use of multi-element filters is a brand new quality
in matching technique. Theory of calculation of these circuits is well known but it has not been used in transducers
matching for years [14]. The calculations of filters were as
sophisticated and difficult, as their manufacturing and measurements were complex. An improvement in computing
and measuring techniques allows for application of
multi-element matching circuits in optimisation of piezoelectric transducers. For acousto-optic devices this method
compensates angular dependence of diffraction efficiency
and acousto-optic characteristics are more flat [7].
Basing on structural and material data of elements used
(transducer, connecting layers, buffer, electrodes and load),
one can calculate electrical characteristics of transducer
(electric impedance) and next, optimal single- or multielement matching circuits of G type and theoretical characteristics of electrical impedance of transducer. This task is
presented in the next section.
3. Procedure for calculating optimal
construction of the modulator
The procedure is performed through a few steps in which
the following parameters are defined: aperture of detector,
central frequency of deflector, transducer length and high,
electric power, and distance between electrodes.
3.1. Aperture of deflector
Aperture (A) of the deflector is limited by attenuation of
acoustic wave in buffer, so
A£
60
ad
a 0 F02
,
(24)
where ad is the acceptable attenuation in aperture region
(ordinary 3 dB), a0 is the coefficient of attenuation of
acoustic wave, and F0 is the approximated central frequency of transducer.
Aperture calculated here is of rather theoretical meaning, since deflector can operate with attenuation even up to
20 dB. This was discussed in a more detailed way in Section 2.2.
3.2. Central frequency of deflector
Central frequency can be calculated assuming larger bandwidth (60%). Since deflectors operate at transitive mode of
diffraction, acoustic beam has some angular divergence
and the largest bandwidth of interaction occurs for Cook’s
parameter Q = 3.7 (see Section 2.2) and equals 0.6 f0 [1].
This frequency band can be obtained using LiNbO3 piezoelectric transducers. Transforming Eq. (7) we have
NV
,
0.6 A
F0 =
(25)
where N is the number of resolved points (determining resolving power of the deflector), V is the speed of acoustic
wave, and A is the size of light beam (aperture) calculated
in previous step.
Three parameters which describe deflector are coupled:
resolution (N), switching rate or aperture (t, A) and a bandwidth (central frequency f0 and parameter Q). So, the procedure of defining central frequency and aperture (steps 1
and 2) must be repeated until they satisfactorily fulfil the
requirements.
3.3. Length of transducer
The optimal length (l) of the transducer can be calculated
from the defined parameter Q (Q = 3.7)
l = 37
.
nV 2
lF02
(26)
where l is the wavelength of light beam, n is the index of
refraction, F0, V are the frequency and the velocity of ultrasound wave.
3.4. Height of transducer
Height of the transducer (d) can be calculated from the condition of divergence of acoustic beam. The height of transducer must assure that the whole aperture should be located
within near field of the transducer
d =
A
V
,
F0
(27)
where the symbols are the same as in Section 3.3.
Opto-Electron. Rev., 11, no. 1, 2003
© 2003 COSiW SEP, Warsaw
Contributed paper
3.5. Required electric power
Electric power depends on efficiency of energy conversion
from electric energy into acoustic one (a) and on depth of
diffraction (h). The following formula describes electric
power
2
54 h d æ l ö
PA = aPE =
ç
÷ ,
M2 l è l0 ø
(28)
where a is the efficiency of energy conversion, PE is the
delivered electric power, l, d are the length and the width
of transducer, respectively, M2 is the relative acousto-optical quality factor of medium (compared to fused
quartz), h is the diffraction depth, l, l1 are the wavelengths of applied light beam and reference laser
(He-Ne), respectively.
3.6. Distance between electrodes H
Intensity distribution of light resulting from phase difference of electric signals in the two paths should assure the
best measurement conditions. This means that in an interference pattern two interference maxima must be apparent.
As a result of theoretical analysis (Eq. 12 and Ref. 15) this
condition is fulfilled when
H = 2.25d,
(29)
where d is the width of the transducer.
Generally, all these optimisation calculations are
difficult, however can be solved with use of our software.
4. Exemplary calculations of two-channel
deflector
Results of calculations are presented in Table 2. The calculations of electric matching were carried out for the transducer attached to a buffer with metallic Cr-Au-In layer
[16]. Optimum radiation of the transducer was calculated
for 220 MHz (central frequency) while maximum of real
part of impedance was found for intermediate frequency of
140 MHz.
Matching was performed with simple single-element
circuits of G type. For matching with circuit a [Fig. 5(a)] it
gave a 3 dB electric band in the range of 124–157 MHz,
while for circuit b [Fig. 5(b)] matching occurred at
117–181 MHz. Although the latter gave larger bandwidth
yet a proper operation of the transducer was not achieved.
Only the use of two-branch LC circuit shown in Fig. 5(c)
resulted in a symmetric electric band larger than necessary
for properly optimised deflector. In table c, attached to
Fig. 5(c), the values of LC elements of the filter are shown.
It was the optimal configuration.
5. Experimental verification
Investigations of modulators were carried on laboratory
stand described in Ref. 17. A PC controlled generator could
precisely change phase of electric signal delivered to the
modulator. The system of recording interference pattern
enabled both on-line operation as well as operation on data
stored earlier in the system memory.
Construction data and experimental errors of phase measurements are shown in Table 3 for preliminary model (described as a model 0) and for models optimised according to
the procedure presented in the paper. The modulators were
Fig. 5. Comparison of transducers matching with use of: single element G type filters (a and b), and two-element filter (c). For the filter c
full matching occurs at band borders (100 and 180 MHz, respectively). Matching with a and b filters is not satisfactory, the use of
four-element filter is much better.
Opto-Electron. Rev., 11, no. 1, 2003
L. Jod³owski
61
Optimisation of construction of two-channel acousto-optic modulator for radio-signal phase detection
Table 2. Results of calculations for the two-channel deflector based on SF 4 glass.
Calculation of aperture
Acceptable attenuation in aperture region
Attenuation coefficient
Central frequency
Calculated admissible aperture
cm
Units used
Values
SI units
dB
5
dB/GHz´cm
110
GHz
0.14
cm
2.1
0.01
km/s
3.89
1.00E+03
2.32
Calculation of F0
Aperture
Velocity of acoustic wave
N (number of points)
500
Calculated F0
MHz
139.26
Optimised length of transducer
Accepted frequency
Refraction index
Wavelength of light beam
Maximum bandwidth (60% for Q = 3.7)
MHz:
84
Calculated length of transducer
mm:
6.78
Accepted length of transducer
Acceptable height of transducer
Accepted height of transducer
mm:
MHz:
140
n
1.685
µm
0.63
mm
6.8
mm
0.77
n(10%)
0.1
quartz –1.56
4.2
1.00E+06
1.00E-06
0.8
Required acoustic power
Modulation depth
Relative acoustic quality
Required acoustic power (eff.: 10 %)
Distance between electrodes
W:
0.3131
mm:
1.8
Q checking:
Q = 3.70778
Bandwidth:
DF (MHz) 84
Calculations were carried out for LiNbO3 transducer (Y 36° cutting – longitudinal wave).
Table 3. Construction data and experimental errors of the phase measurements for four modulators.
Parameters
Optimised models
Model 0
1
Material of buffer
BK 7
SF 4
Transducer
2
3
BK 7
BK 7
LiNbO3 (Y 36°)
Central frequency (MHz)
140
Dimensions of electrode (length ´ height) (mm)
10´1
6.8´0.8*
Distance between electrodes** (mm)
3
1.8
Theoretical coefficient
6
4.5
Measurement coefficient
3.78
2.95
3.15
3.65
Amplitude of correction function (°)
15.5
1.4
5.3
9.74
3
<0,5
<0,5
2
Error of phase measurement (°)
* value calculated theoretically, precision of electrodes performance was not high.
** measured between electrodes centres.
62
Opto-Electron. Rev., 11, no. 1, 2003
© 2003 COSiW SEP, Warsaw
Contributed paper
manufactured at the Department of Acousto-optic Modulators in Institute of Optoelectronics. LiNbO3 crystal plates attached to SF4 and BK7 glass buffers were used as piezoelectric transducers.
Compared to preliminary model, optimised modulators
are characterised by considerably lower level of cross-talk
energy and significant increase in phase resolution. In two
cases experimental errors in phase measurements at frequency 140 MHz were lower than 0.5°.
6. Conclusions
Presented method for calculation of two-channel acousto-optic deflectors completes existing literature devoted to
acousto-optic deflectors. A two-channel modulator is a key
element in any acousto-optical receiver used in spectrum
analysers. The paper shows construction of a device for
spectrum and signal phase measurements at frequency
bandwidth of 80 MHz with resolution of 0.2 MHz. Such
device can be based on a cheap acousto-optic deflector
made of SF4 glass.
Research on modulators performed in Institute of Optoelectronics confirms high accuracy of the phase measurement of radio-signals. Those modulators can be used for
analysis and recognition of signals in mobile phones networks (digital GSM, analogue NMT) or UHF band.
References
1. W.I. Balakszij, W.N. Parygin, and L.E. Czirkow, Fizitcheskiye Osnovy Akustooptiki, Radio i Swiaz, Moscow,
1985. (in Russian).
2. A. Sliwinski, Ultrasouds and their Applications, WNT,
Warsaw, 1993. (in Polish)
3. W. Ciurapiñski and M. Szustakowski: “Acousto-optic RF
analyser”, Proc. Acousto-electronics 87 Varna, May 5-8,
359–362 (1997). (in Russian).
Opto-Electron. Rev., 11, no. 1, 2003
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63
EMIS Datareviews Series
Electronic Materials Information Service and
related publications
Series Advisor: Professor B.L Weiss-University of Surrey, UK
EMIS DATAREVIEWS SERIES
This series comprises books on semiconductors and other electronic materials. These adopt a unique editorial approach based
wholly on commissioned input from experts around the world into a structured framework. Each book comprises numerous invited Datareviews (i.e. modules of knowledge) and combines latest specialised understanding, highly structured presentation, numeric data, individual Datareview cut-off dates, background and contextual information, expert guidance to the literature, wide but
deep coverage and comprehensive subject indexing. All EMIS books are casebound, 280 x 210 mm.
Properties, growth and applications of diamond
M.H. Nazare and A.J. Neves (Eds.)
Recent breakthroughs in the synthesis of diamond have led to
increased availability at lower cost. This has spurred R&D into
its characterisation and application in machine tools, optical
coatings, X-ray windows and light-emitting optoelectronic devices. In the longer term, diamond’s high thermal conductivity
and electron mobility make it potentially useful for integrated
circuit applications (e.g. in heat sinks). This book draws together expertise from some 60 researchers in Europe and the
USA working on bulk and thin film diamond. All fully-refereed,
the contributions are combined to form a highly structured volume with reviews, evaluations, tables and illustrative material,
together with expert guidance to the literature.
EM 026, 550 pages,
1SBN 0 85296 7853, 2001
£135
Physical properties of liquid crystals: Nematics
D.A. Dunmur, A. Fukuda and G.R. Luckhurst (Eds.)
The demand for liquid crystals with better display parameters
and lower power consumption has stimulated much research
into their properties and characterisation. A large team of some
60 leading researchers from the USA, Europe and Japan have
focused their expertise to extract and review data on a wide
range of properties of nematics, including those which are essential to the development of all types of liquid crystal device.
Where appropriate these properties are also explained with expert commentary. The book is fully illustrated and structured
for reference.
EM 025, 696 pages,
ISBN 0 85296 7845, 2000
£165
Properties, processing and applications of glass and
rare earth-doped glasses for optical fibres
D.W. Hewak (Ed.)
REtD on optical fibres is driven by the need for ever higher
bandwidth transmission in telecommunications at lower cost.
Some 60 experts from leading R&D groups around the world
review silica, oxide, halide and chalcogenide glasses in a
structured format, thereby creating an authoritative, encyclopaedic reference source for researchers and engineers. The
book includes a historical overview by W. Alexander Gambling,
FRS. Over 60 individually-authored modules on the abovementioned types of glass covering optical, thermal and mechanical properties, RE spectroscopy, optical fibre manufacture and applications in fibre amplifiers, fibre gratings, fibre lasers and optical switches.
EM 022, 395 pages,
SBN 0 85296 952 X, 1998
£125
Properties, processing and applications of indium
phosphide
T.P. Pearsall (Ed.)
In 1991, in response to strong demand by semiconductor researchers, the IEE published ‘Properties of Indium Phosphide’.
Since then InP has continued to be the subject of intensive
R&D, especially in the area of optoelectronics, with over 11,000
papers published in the intervening period. Professor Pearsall
has assembled a team of some 20 researchers from around
the world in order to identify the significant advances and distil
the current knowledge from this large mass of literature. New
text, tables and illustrations, which form the bulk of the book,
are presented together with some compressed material from
the old volume.
EM 021, 300 pages,
ISBN 0 85296 949 X, 2000
£95
Properties of crystalline silicon
R. Hull (Ed.)
Silicon, as used in silicon chips, is the material on which the
information society depends for its power to process information. In 1988 INSPEC published the standard reference
source on silicon properties and since then an enormous
amount of Si R&D has taken place, with a hundred thousand
papers published over 1989-1998. Now, for the benefit of academics, process developers and device simulation engineers
working in the area of silicon microelectronics Professor Hull
has brought together the specialised expertise of over 100 invited authors from the USA, Japan and Europe coordinated
by 18 chapter editors to concisely review its properties in a
structured way.
EM 020, 1042 pages,
ISBN 0 85296 933 3, 1999
£195
Properties of amorphous silicon and its alloys
T.M. Searle (Ed.)
Over the last decade there have been major advances in the
characterisation of amorphous silicon for use in solar cells, TFT
liquid crystal displays, photodetectors, LEDs and xerographic
devices. In the last decade, researchers have succeeded in
dispelling much of the uncertainty about its behaviour and the
associated models, so that engineers are better able to exploit
it. Here the essential knowledge of the properties, preparation
and exploitation of amorphous silicon are distilled into one volume.
EM 019, 440 pages
ISBN 0 85296 922 8, 1998
£135
http://www.iee.org.uk/publish/books/emis.html
64
Opto-Electron. Rev., 11, no. 1, 2003
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